The invention relates to an apparatus and method for generating sinusoidal signals that are modulated under control of a signal which is conditioned to perform a certain task.
Specifically, the invention relates to an apparatus and method for generating sinusoidal signals which are variable in a particular parameter, such as frequency, from one time frame to another time frame, or from one sampling interval to another sampling interval. A representative application of the present invention is generation of a sinusoidal signal which is appropriate as a pitch component upon vocal tract information which may be imposed to reproduce speech information.
Earlier sinusoidal signal generating apparatus and methods often have involved a pure pulse approach in order that the signal could be digitized. However, a problem with such a pure pulse approach is that the required data manipulations can occur only at specified points in time. Thus, adjacent samples may have sufficiently different frequencies that no smooth transition is achievable between samples.
The improved apparatus and method disclosed for generating sinusoidal signals enables generation of a mathematically continuous (as opposed to a discrete sample represented) signal. Such a continuous mathematical signal can be finessed from period to period (i.e., sample to sample) to provide smooth segues in the varying signal parameter (e.g., frequency).
Thus, the present invention provides an apparatus and method for producing a sinusoidal signal and calculating transitions of a parameter "on the fly" from a first value to a second value. The preferred parameter illustrated in this application is frequency, but the approach and model disclosed apply equally well for any sinusoidal parameter.